exp_ch8.adb   [plain text]

--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                              E X P _ C H 8                               --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 1992-2004 Free Software Foundation, Inc.          --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
-- MA 02111-1307, USA.                                                      --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --

with Atree;    use Atree;
with Einfo;    use Einfo;
with Exp_Dbug; use Exp_Dbug;
with Exp_Util; use Exp_Util;
with Freeze;   use Freeze;
with Nlists;   use Nlists;
with Sem;      use Sem;
with Sem_Ch8;  use Sem_Ch8;
with Sinfo;    use Sinfo;
with Stand;    use Stand;
with Targparm; use Targparm;

package body Exp_Ch8 is

   -- Expand_N_Exception_Renaming_Declaration --

   procedure Expand_N_Exception_Renaming_Declaration (N : Node_Id) is
      Decl : constant Node_Id := Debug_Renaming_Declaration (N);

      if Present (Decl) then
         Insert_Action (N, Decl);
      end if;
   end Expand_N_Exception_Renaming_Declaration;

   -- Expand_N_Object_Renaming_Declaration --

   --  Most object renaming cases can be done by just capturing the address
   --  of the renamed object. The cases in which this is not true are when
   --  this address is not computable, since it involves extraction of a
   --  packed array element, or of a record component to which a component
   --  clause applies (that can specify an arbitrary bit boundary), or where
   --  the enclosing record itself has a non-standard representation.

   --  In these two cases, we pre-evaluate the renaming expression, by
   --  extracting and freezing the values of any subscripts, and then we
   --  set the flag Is_Renaming_Of_Object which means that any reference
   --  to the object will be handled by macro substitution in the front
   --  end, and the back end will know to ignore the renaming declaration.

   --  An additional odd case that requires processing by expansion is
   --  the renaming of a discriminant of a mutable record type. The object
   --  is a constant because it renames something that cannot be assigned to,
   --  but in fact the underlying value can change and must be reevaluated
   --  at each reference. Gigi does have a notion of a "constant view" of
   --  an object, and therefore the front-end must perform the expansion.
   --  For simplicity, and to bypass some obscure code-generation problem,
   --  we use macro substitution for all renamed discriminants, whether the
   --  enclosing type is constrained or not.

   --  The other special processing required is for the case of renaming
   --  of an object of a class wide type, where it is necessary to build
   --  the appropriate subtype for the renamed object.
   --  More comments needed for this para ???

   procedure Expand_N_Object_Renaming_Declaration (N : Node_Id) is
      Nam  : constant Node_Id := Name (N);
      T    : Entity_Id;
      Decl : Node_Id;

      procedure Evaluate_Name (Fname : Node_Id);
      --  A recursive procedure used to freeze a name in the sense described
      --  above, i.e. any variable references or function calls are removed.
      --  Of course the outer level variable reference must not be removed.
      --  For example in A(J,F(K)), A is left as is, but J and F(K) are
      --  evaluated and removed.

      function Evaluation_Required (Nam : Node_Id) return Boolean;
      --  Determines whether it is necessary to do static name evaluation
      --  for renaming of Nam. It is considered necessary if evaluating the
      --  name involves indexing a packed array, or extracting a component
      --  of a record to which a component clause applies. Note that we are
      --  only interested in these operations if they occur as part of the
      --  name itself, subscripts are just values that are computed as part
      --  of the evaluation, so their form is unimportant.

      -- Evaluate_Name --

      procedure Evaluate_Name (Fname : Node_Id) is
         K : constant Node_Kind := Nkind (Fname);
         E : Node_Id;

         --  For an explicit dereference, we simply force the evaluation
         --  of the name expression. The dereference provides a value that
         --  is the address for the renamed object, and it is precisely
         --  this value that we want to preserve.

         if K = N_Explicit_Dereference then
            Force_Evaluation (Prefix (Fname));

         --  For a selected component, we simply evaluate the prefix

         elsif K = N_Selected_Component then
            Evaluate_Name (Prefix (Fname));

         --  For an indexed component, or an attribute reference, we evaluate
         --  the prefix, which is itself a name, recursively, and then force
         --  the evaluation of all the subscripts (or attribute expressions).

         elsif K = N_Indexed_Component
           or else K = N_Attribute_Reference
            Evaluate_Name (Prefix (Fname));

            E := First (Expressions (Fname));
            while Present (E) loop
               Force_Evaluation (E);

               if Original_Node (E) /= E then
                  Set_Do_Range_Check (E, Do_Range_Check (Original_Node (E)));
               end if;

               Next (E);
            end loop;

         --  For a slice, we evaluate the prefix, as for the indexed component
         --  case and then, if there is a range present, either directly or
         --  as the constraint of a discrete subtype indication, we evaluate
         --  the two bounds of this range.

         elsif K = N_Slice then
            Evaluate_Name (Prefix (Fname));

               DR     : constant Node_Id := Discrete_Range (Fname);
               Constr : Node_Id;
               Rexpr  : Node_Id;

               if Nkind (DR) = N_Range then
                  Force_Evaluation (Low_Bound (DR));
                  Force_Evaluation (High_Bound (DR));

               elsif Nkind (DR) = N_Subtype_Indication then
                  Constr := Constraint (DR);

                  if Nkind (Constr) = N_Range_Constraint then
                     Rexpr := Range_Expression (Constr);

                     Force_Evaluation (Low_Bound (Rexpr));
                     Force_Evaluation (High_Bound (Rexpr));
                  end if;
               end if;

         --  For a type conversion, the expression of the conversion must be
         --  the name of an object, and we simply need to evaluate this name.

         elsif K = N_Type_Conversion then
            Evaluate_Name (Expression (Fname));

         --  For a function call, we evaluate the call

         elsif K = N_Function_Call then
            Force_Evaluation (Fname);

         --  The remaining cases are direct name, operator symbol and
         --  character literal. In all these cases, we do nothing, since
         --  we want to reevaluate each time the renamed object is used.

         end if;
      end Evaluate_Name;

      -- Evaluation_Required --

      function Evaluation_Required (Nam : Node_Id) return Boolean is
         if Nkind (Nam) = N_Indexed_Component
           or else Nkind (Nam) = N_Slice
            if Is_Packed (Etype (Prefix (Nam))) then
               return True;
               return Evaluation_Required (Prefix (Nam));
            end if;

         elsif Nkind (Nam) = N_Selected_Component then
               Rec_Type : constant Entity_Id := Etype (Prefix (Nam));

               if Present (Component_Clause (Entity (Selector_Name (Nam))))
                 or else Has_Non_Standard_Rep (Rec_Type)
                  return True;

               elsif Ekind (Entity (Selector_Name (Nam))) = E_Discriminant
                 and then Is_Record_Type (Rec_Type)
                 and then not Is_Concurrent_Record_Type (Rec_Type)
                  return True;

                  return Evaluation_Required (Prefix (Nam));
               end if;

            return False;
         end if;
      end Evaluation_Required;

   --  Start of processing for Expand_N_Object_Renaming_Declaration

      --  Perform name evaluation if required

      if Evaluation_Required (Nam) then
         Evaluate_Name (Nam);
         Set_Is_Renaming_Of_Object (Defining_Identifier (N));
      end if;

      --  Deal with construction of subtype in class-wide case

      T := Etype (Defining_Identifier (N));

      if Is_Class_Wide_Type (T) then
         Expand_Subtype_From_Expr (N, T, Subtype_Mark (N), Name (N));
         Find_Type (Subtype_Mark (N));
         Set_Etype (Defining_Identifier (N), Entity (Subtype_Mark (N)));

         --  Freeze the class-wide subtype here to ensure that the subtype
         --  and equivalent type are frozen before the renaming. This is
         --  required for targets where Frontend_Layout_On_Target is true.
         --  For targets where Gigi is used, class-wide subtype should not
         --  be frozen (in that case the subtype is marked as already frozen
         --  when it's created).

         if Frontend_Layout_On_Target then
            Freeze_Before (N, Entity (Subtype_Mark (N)));
         end if;
      end if;

      --  Create renaming entry for debug information

      Decl := Debug_Renaming_Declaration (N);

      if Present (Decl) then
         Insert_Action (N, Decl);
      end if;
   end Expand_N_Object_Renaming_Declaration;

   -- Expand_N_Package_Renaming_Declaration --

   procedure Expand_N_Package_Renaming_Declaration (N : Node_Id) is
      Decl : constant Node_Id := Debug_Renaming_Declaration (N);

      if Present (Decl) then

         --  If we are in a compilation unit, then this is an outer
         --  level declaration, and must have a scope of Standard

         if Nkind (Parent (N)) = N_Compilation_Unit then
               Aux : constant Node_Id := Aux_Decls_Node (Parent (N));

               New_Scope (Standard_Standard);

               if No (Actions (Aux)) then
                  Set_Actions (Aux, New_List (Decl));
                  Append (Decl, Actions (Aux));
               end if;

               Analyze (Decl);

         --  Otherwise, just insert after the package declaration

            Insert_Action (N, Decl);
         end if;
      end if;
   end Expand_N_Package_Renaming_Declaration;

end Exp_Ch8;